Electrolytic phosphating treatment method and warm or hot forging method

ABSTRACT

The invention provides an electrolytic phosphating treatment method that forms a film by causing a large current to flow at a voltage as low as possible and can improve efficiency. Namely, the invention provides an electrolytic phosphating treatment method for forming a film containing a metal precipitating from a nitrate, and a phosphate, by executing electrolysis between a metal that is the same as a metal of a nitrate of a treatment bath as an electrode and a work by using a D.C. power source, the treatment bath comprising phosphoric acid, zinc, iron or manganese as a metal capable of dissociating phosphoric acid and dissolving in phosphoric acid, and a solution dissolving a nitrate of a metal to become a film component, wherein anions other than nitrate ions and metal ions other than the metal ions to become the film component are present at not greater than 0.5 g/L, the metal ion dissolving from the nitrate is present at greater than 10 g/L and phosphoric acid and phosphate ion are present at not greater than ½ of the metal ion dissolving from the nitrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a treatment bath for forming a film containing a phosphate and a metal on a metal surface by an electrolytic treatment, a method for this treatment, and a lubrication treatment for plastic working in which a work is heated to a high temperature and to above a temperature for warm or hot forging.

2. Description of the Related Art Japanese Unexamined Patent Publication (Kokai) No. 2000-234200 (JP-A-2000-234200) is a basic patent application regarding an electrolytic phosphating treatment and was filed by a present inventor. The feature of this patent application resides in that a treatment bath does not substantially contain metal ions other than film forming components (below 0.4 g/L). The feature of the treatment bath composition is that it contains 6 to 140 g/L of nitrate ion, 0.5 to 60 g/L of phosphoric acid and phosphate ion, 0.5 to 70 g/L of those ions which form a complex with the phosphate ion inside the treatment bath and dissolve therein (such as zinc ion) and 0 to 40 g/L of metal ions that precipitate when dissolved ions are reduced and precipitate.

In Examples 1, 3 and 4 of the patent JP-A-2000-234200, an electrolytic voltage is 9.6 V or above when a current of at least 1 A/dm² is caused to flow (one work is calculated at 2 dm²) and as far as a cathodic treatment is concerned, it is at least 17.7 V.

Japanese Unexamined Patent Publication (Kokai) No. 2002-322593 (JP-A-2002-322593) is a patent application, also filed by the present inventors, regarding an electrolytic phosphating treatment. Whereas JP-A-2000-2343200, described above, has a feature that reaction impeding substances (that is, metal ions other than film forming components) are not allowed to be contained from outside into the phosphating treatment bath, JP-A-2002-322593 relates to a invention in which the formation of the impeding substance ions (N₂O₄ gas, excessive Fe ion), inside the reaction system, is controlled.

The qualitative composition dissolved in the treatment bath in JP-A-2002-322593 is the same as that of JP-A-2000-234200. The treatment bath compositions of all Examples restrict the reduced and precipitating metal ions to a range of 4.7 to 7.3 g/L which is below 10 g/L. In all Examples, the electrolysis is executed at a voltage of at least 8 V.

Japanese Unexamined Patent Publication (Kokai) No. 2004-52085 (JP-A-2004-52085) also relates to a invention regarding an electrolytic phosphating treatment filed by the present inventors. In JP-A-2004-52085, washing water, used after the phosphating treatment, is subjected to electro-dialysis and the concentrated portion is again returned to the treatment bath, and findings about the electrolysis of the treatment bath components are acquired.

FIG. 3 of JP-A-2004-52085 indicates that the electrolysis in the electro-dialysis bath containing the electrolytic treatment bath components is observed in two forms. In other words, electro-dialysis at an impressed voltage of 6 V or below is ion migration of only solute components but involves electrolysis of water as a solvent at a voltage of 6 V or above. The reference points it out that the electrolysis at 6 V or above may form sludge with the decomposition of water.

The illustration shown in FIG. 3 indicates that 10 electrolytic baths are stacked and two electrolytic systems exist with 0.6 V as the boundary per electrolytic bath.

Namely, JP-A-2004-52085 indicates that the electrolytic phosphating treatment is constituted by two electrolytic systems with respect to a change of the voltage. FIG. 3 demonstrates that a current (X axis)—voltage (Y axis) relation of a lower electrolytic voltage system has a smaller gradient than that of a higher electrolytic voltage system and has higher electrolytic efficiency.

The electrolytic treatment at the lower voltage suppresses the decomposition of water as the solvent and preferentially moves the solute components, thereby improving film formation efficiency.

On the other hand, a working technology called “warm or hot forging” is known that heats a metal material to 200° C. or above and subjects it to plastic working. This working technology has widely been employed for a variety of metal materials such as iron and steel, aluminum and its alloys, magnesium and its alloys, and so forth.

Japanese Unexamined Patent Publication (Kokai) No. 6-1994 (JP-A-6-1994) relates to a lubrication treatment for cold forging of steel materials. As problems in the prior art technologies, this reference describes that warm forging is carried out by heating a work to 400 to 1,000° C. and conducting forging but that a suitable lubricant and treatment method are not known.

In cold forging, a method of forming a lubrication film that forms a phosphating treatment film on a work, immerses the work into an organic fatty acid salt bath (such as sodium stearate) and forms a lubrication film has been established as the lubrication treatment. In other words, a method that subjects the work to a lubrication treatment using a phosphating treatment film has been established.

In contrast, in warm or hot forging according to the prior art, the method that forms the phosphating treatment film on the work and forms a film using a lubricant on the former has not been carried out for the following reasons. Namely, the phosphating treatment film formed by a non-electrolytic system according to the prior art cannot secure adhesion to a foundation metal within the temperature range (about 400 to 1,000° C.) for warm forging. The lubrication film is destroyed and does not operate as the lubrication treatment. The role of the lubrication treatment is to interpose a lubricant between a die and a work and to prevent direct contact between the mold and the work. However, it is difficult to secure such a function unless adhesion of the phosphating treatment film is secured at the temperature of warm forging.

Therefore, warm or hot forging according to the prior art employs the following steps. A work is first heated to about 250 to 300° C. and is immersed immediately thereafter into a liquid having dispersed therein a solid -lubricant such as graphite, or is sprayed with a liquid containing graphite powder, to form a graphite film on the surface of the work. The work is subsequently heated to about 800° C. and (warm forging) pressing is successively conducted. In this case, another lubricant is separately sprayed to the surface of the mold for mold lubrication. Other methods have also been conducted that do not apply the lubricant to the work and simply spray the lubricant into the mold.

According to the method that applies only the lubricant to the work, the lubricant merely adheres physically to the work. Because the lubricant does not adhere to the work with a chemical reaction, the lubricant is easily removed, at a machining portion, when the mold and the work undergo strong friction or squeezing at the working portion during machining. In this case, seizure occurs at that portion.

In JP-A-6-1994, the work is immersed in a solution consisting of water-soluble inorganic salts (K₂SO₄, Na₂B₄O₄, etc) and molybdenum disulfide and/or graphite to uniformly apply the lubricant on the surface of the work, then the work is dried, and a lubrication film consisting of the inorganic salt, molybdenum disulfide and/or graphite is formed on the surface of the work. The method of this reference requires the step of washing the work with hydrofluoric acid and nitric acid in the production steps of the lubrication film. This pickling is directed to form a firm film on the surface. The specification describes that the lubrication film so formed exhibits a lubrication function for warm forging. However, the film is not formed by allowing it to react with the surface of the work but merely causes the solid components in the treatment bath to physically adhere to the chemically active surface.

JP-A-2000-234200 filed by the present inventors describes an invention relating to a phosphating treatment film as a foundation film to be formed on various kinds of works for forging. However, the reference discloses only a phosphate+metal film that is applied to a coating foundation and improves coating corrosion resistance and a formation example of a phosphating treatment film consisting only of a phosphate that is applied to cold forging. The reference does not describe or suggest the application of the phosphate+metal film to warm or hot forging.

In other words, the basic element of the electrolytic phosphating treatment technology described in JP-A-2000-234200 is that the treatment bath substantially does not contain metal ions that do not become the film component (below 400 ppm). The reference describes that the forms of the film include the case where metals that do not become the phosphate are contained (claim 36, Examples 1, 4 and 5) and the case where metals that do not become the phosphate are not contained (claim 8, Example 2).

When the treatment bath contains the metal that does not become the phosphate, the film is the film constituted as a phosphate+metal. The metal contained in the film is the metal that has existed as the cation in the solution is reduced and precipitated. The reference discloses that when the film constituted by a phosphate+metal is employed for the coating foundation treatment, the coating corrosion resistance can be improved. The reference clearly states that precipitation of the metal is made as the metal ion dissolved in the solution is reduced and precipitated. The reference further describes that to reduce and precipitate the metal, it is necessary for the treatment bath to not contain metal ions that do not become the film components (such as sodium ion). This also indicates that the formation of the film constituted by phosphate+metal is not possible from a non-electrolytic treatment bath containing those metal ions which do not operate as the film components. The reference represents that the difference of such a foundation film invites a difference of corrosion resistance in the coat.

JP-A-2000-234200 has an Example (Example 2) used for cold forging. The reference indicates that the treatment bath composition, as well as the film composition, are drastically different between an Example for cold forging and Example for coating. The reference further represents that the metal components other than the phosphate are contained for coating foundation but the metal components other than the phosphate are contained only slightly for cold forging foundation.

Table 1 shows the comparison about the treatment method, the application, the treatment bath composition and the film composition in the Examples and the Comparative Examples of the patent reference described above. TABLE 1 treatment method, treatment film electrolytic bath composition or non- composition ratio electrolytic application Ni/H₃PO₄:(g/L) Ni/P: Wt % remarks Example 1 electrolytic coating 5.5/7.6 = 0.72 1.9-2.1 corrosion foundation resistance: Comparative electrolytic coating 0.5/7 = 0.07 0.01-0.12 Example 1 > Example 1 foundation Comparative Example 1 Example 2 electrolytic cold forging 0.25/21.2 = 0.01 0 foundation Comparative non- cold forging — 0 Example 2 electrolytic foundation Example 4 electrolytic coating 3.8/2.8 = 1.36 0.51-0.75 foundation Example 5 electrolytic coating 3.9/2.8 = 1.39 0.77-0.94 foundation

The following can be confirmed from the comparison tabulated above.

i. The film for cold forging is a film that does not contain a metal component (Ni) that does not becomes a phosphate.

ii. Coating corrosion resistance is higher in the film containing the metal component (Ni) that does not become the phosphate.

In other words, the film not containing the metal component that does not become the phosphate is suitable for the lubrication treatment for cold forging (at a low temperature) but a film containing the metal component is suitable for the coating corrosion resistance. This difference corresponds to the fact that the function of the phosphating treatment film is different between the coating foundation and lubrication for cold forging.

Next, the reason why the phosphating treatment film not containing Ni of the prior art has been used for the lubrication treatment for cold forging will be clarified. The lubrication function for cold forging is exhibited when a lubrication film (foundation film: phosphate+lubricant (sodium stearate, etc)) covering the surface of the work is melted and starts fluidizing to thereby prevent direct contact between the work and a mold in cold forging where the mold and the work for forging (steel) come into mutual contact within a temperature range (150 to 250° C.) for cold forging and the work undergoes plastic change. Therefore, performance items required for the foundation film are a. a chemical property capable of uniformly retaining the lubricant, that is, to secure chemical affinity with the lubricant: and b. the film starts fluidizing in such a fashion as to correspond to the change of the work within the temperature range (150 to 250° C.) of cold forging. The requirement (a) described above can be secured by the phosphate treatment film “not containing metals reduced and precipitating” of the prior art. The requirement (b) can be secured by the phosphate film that does not contain Ni.

In the film formed by the non-electrolytic treatment system, the treatment bath is limited so as to secure the performances (a) and (b). In other words, the “reduced and precipitating metal” (generally, Ni) is limited to 0.5 g/L or below. The phosphating treatment film for cold forging formed by the non-electrolytic system of the prior art is the film that does not basically contain Ni or the film that does not allow the activity of Ni, and satisfies the performances (a) and (b) described above inside the cold forging temperature range. In the non-electrolytic system, it is basically impossible to precipitate the “reduced and precipitating metal”. In the non-electrolytic treatment system, therefore, a thick film containing Ni and suitable for forging (having a deposition amount of at least 5 g/m², for example) cannot be formed because the electrolytic reaction voltage is lower than the decomposition voltage of water.

On the other hand, the film formed by the electrolytic treatment method can precipitate the “reduced and precipitating metal”. That is, the film can contain, or does not contain, the metal Ni having a high melting point (melting point: 1,453° C.) in the form of a chemical reaction in the work. However, when a large amount of the “reduced and precipitating metal” such as Ni is contained, the phosphate treatment film does not satisfy the performances (a) and (b) required for cold forging of the steel. Therefore, such a film is not applied to cold forging.

In Examples tabulated in Table 1, those examples in which the coating corrosion resistance is improved (Examples 1, 4 and 5) are all contain a large amount of the metal Ni. This represents that the coating foundation film is preferably the one that contains a large mount of the metal Ni precipitating with the change of the charge and is strongly bonded to the foundation support metal.

The phenomenon associated with the coating corrosion resistance and its evaluation is conducted under normal atmospheric pressure and ambient temperature conditions. Cracking and degradation of the coat, to which the foundation film contributes, is less when the phosphating treatment film is not bonded chemically strongly to the metal blank. The bonding strength between the metal blank and the phosphating treatment film becomes greater in association with the magnitude of activation energy related with the film formation reaction. Precipitation of the “reduced and precipitating metal” involves a change in the charge. In contrast, “precipitation of the phosphate crystal” is formed by the reaction that does not involve the change of the charge of the metal ions. Activation energy of both reaction systems is different and the precipitation reaction of the “reduced and precipitating metal” is greater. This corresponds to the fact that the film containing a greater amount of Ni as the “reduced and precipitating metal” is strongly bonded to the foundation metal in the formation of the phosphating treatment film. The result tabulated in Table 1 evidences this fact.

In the lubrication treatment associated with cold forging, high adhesion between the phosphating treatment film and the foundation metal is not advantageous. In the lubrication treatment, the surface must involve fluidity with the plastic change of the blank metal. The lubrication property is the operation that prevents the metal (press mold) and the metal (blank) from coming into direct contact with each other. The film firmly bonded to the foundation metal is likely to undergo a plastic change while integrated with the foundation metal blank. Consequently, fluidity is lost and the lubrication property drops.

The concept of the lubrication treatment in cold forging can be applied to warm forging, too. In other words, the phosphating treatment film requiring the lubrication performance and used for warm forging preferably has fluidity without being integrated with the metal blank in its plastic working temperature and pressure range. That is to say, adhesion with the foundation metal preferably drops in the temperature and pressure range of warm forging.

In the temperature range (150 to 250° C.) of cold forging, therefore, the film not containing and, basically, the “reduced and precipitating metal” is suitable. As to the retention of the lubrication performance in warm forging for plastic working after the work is heated, however, the film containing the “reduced and precipitating metal” can be employed.

As explained above, the phosphating treatment film containing the precipitating metal and formed by the electrolytic phosphating treatment does not have lubrication performance in the temperature range of cold forging (150 to 250° C.). JP-A-2000-234200 illustrates the film to be applied to cold forging but does not teach or suggest the possibility of the application to warm or hot forging.

SUMMARY OF THE INVENTION

It is a main object of the present invention to level up the electrolytic phosphating treatment technology.

That is,

(i) To clarify an efficient control method of the electrolytic treatment technology and to improve reaction efficiency; and

(ii) To make the electrolytic phosphating treatment technology more efficient than the prior art technology into practical application and to expand the application range.

In other words, the object of the invention is to apply the technology to warm or hot forging lubrication treatment.

The first object, i.e. “to clarify an efficient control method of the electrolytic treatment technology and to improve reaction efficiency”, will be explained.

The inventor of the present invention classifies the phosphating treatment bath into a “treatment bath for forming a film mainly formed of a phosphate” and a “treatment bath for forming a film of a metal+a phosphate”. This concept has already been explained by the present inventor in the first patent document described above.

The “treatment bath for forming a film mainly formed of a phosphate” is composed of phosphoric acid and a solution that contains “zinc, iron or manganese as a metal dissolved in a phosphoric acid solution and capable of dissociating and dissolving phosphoric acid” as main components and also contains a “nitrate of a metal which is to become a film component”.

The “treatment bath for forming a film of a metal+a phosphate” is a treatment bath constituted by “phosphoric acid”, “zinc as a metal dissolved in a phosphoric acid solution and capable of dissociating and dissolving phosphoric acid” and a solution dissolving “a nitrate of a metal that is to become a film component”.

The former treatment bath is an ordinary treatment bath in the non-electrolytic treatment according to the prior art. The present invention is directed to the latter.

The object, i.e. “to clarify an efficient control method of the electrolytic treatment technology and to improve reaction efficiency”, is to form a film by causing a large current to flow at a voltage as low as possible. That is, it means the formation of the film with small electric energy.

The object “to expand the application range, that is, to apply the treatment to the lubrication treatment for warm forging”, means the application of the present technology to the lubrication treatment for warm or hot forging that has scored no actual record in the past.

Another object of the invention is to level up the lubrication treatment in forging in which a work is heated from room temperature to 200° C. or more. More specifically, a lubrication treatment film capable of withstanding heating to 200° C. or above (that is, the lubrication film does not peel off from the work even when the temperature reaches a predetermined heating temperature) is formed on the surface of the work and the lubrication treatment is carried out. Such a lubrication treatment is carried out by “a foundation film having adhesion with a foundation metal material and capable of retaining a lubricant” and “a layer (film) of a lubricant exhibiting a lubrication function to a mold and to the work at a heated temperature”.

A concrete method of such a lubrication treatment varies depending on an individual metal material. For, physical and chemical properties are different depending on the individual material. However, the concept of the lubrication treatment described above (formation of the lubrication film constituted by the heat resistant foundation film and the lubrication layer) is common irrespective of the difference of the materials.

Lubricants have been used in the past for warm forging. Under such circumstances, the problem that the present invention is to solve is the formation of a foundation film having a heat resistance to various works to be forged.

Warm forging has been most widely applied to steel materials. In the case of the application to steel, the object of the invention is to provide an excellent lubrication treatment in a warm forging temperature range of 400° C. or above. This object can be achieved by uniformly forming a phosphating treatment film consisting of “phosphate+metal” on the surface of a work that is to be heated to 400° C. or above and further forming a lubrication film formed of a lubricant having excellent lubrication performance at 400° C. or above on the phosphating treatment film.

As described above, the problem that the invention is to solve is to form the strong heat resistant film (treatment film) bonding chemically strongly to the surface of the work and the lubrication treatment film supporting thereon the lubricant and to apply this film to the lubrication treatment for warm forging.

The object “to improve electrolytic reaction efficiency” is to cause a large current to flow at a low voltage by decreasing an electric resistance of an electrolytic treatment reaction system.

The flows of current and ions in the electrolytic treatment will be explained with reference to FIG. 1. It will be assumed hereby that the electric resistance does not exist in between a D.C. power source; and an electrode or a work.

The resistance occurs at the following three points in the electrolytic treatment system described above. (i) conversion on electrode surface (electrode and treatment bath): conversion of current→ion migration, (ii) stability of a solution state inside treatment bath and ion migration, and (iii) conversion on work surface: conversion from solution (ion)→solid (film) : film formation.

These three points will be explained.

(i) Conversion on electrode surface: conversion of current→ion migration

It is necessary that the current easily moves to the dissolved ion from the electrode. The ion that is mainly to be moved is preferably a film forming component. The film that the invention is to form is a “phosphate film containing a metal”. Therefore, it is preferred that the electrode material is the same as the main component of the treatment bath that precipitates from the treatment bath and becomes a film. In other words, a metal that becomes the film component is preferably used as the electrode. As the metal that becomes the film component is a nitrate and is contained in the treatment bath, the electrode material is a metal composed of the nitrate contained in the treatment bath.

Incidentally, in the electrolytic phosphating treatment, all the currents associated with the electrode are not always consumed for dissolution. This is different from electro-plating. In the electrolytic phosphating treatment, the same metal component as the electrode material is separately supplied in the dissolved form (metal ion) into the treatment bath. Therefore, the current impressed is divided into a portion of “dissolution of electrode material” and a “portion directly associated with migration of treatment bath component and executing reaction of component ion”.

The technical meaning of “improvement of electrolytic reaction efficiency” is to increase the proportion of the portion that “directly participates in the movement of the treatment bath components and executes the reaction of the component ion”, and controls the reaction. The use of the same metal as the metal nitrate to be added to the treatment bath for the electrode material is effective for the operation described above.

In electric plating, however, the case where such metal ions are supplied as the chemical does not exist. Therefore, the impressed current is fully consumed for dissolving the electrode material.

(ii) Stability of a solution state inside treatment bath and ion migration

The main anion components of the treatment bath of the present invention are only the phosphate ion and the nitrate ion. The relation of solubility between the phosphate ion and the nitrate ion is nitrate ion>phosphate ion. Therefore, a solution containing a greater amount of the nitrate ion is more advantageous from the aspect of solubility.

In the present invention, the condition of the treatment bath of the nitrate ion>phosphate ion is expressed by the proportion by setting the metal ion from the nitrate to 10 g/L and limiting phosphoric acid and phosphate ion to not greater than ½ of the former. In this way, the concentration of the nitrate ion and the proportion of the nitrate ion to the phosphate ion are clarified. The invention further represents that in the treatment bath, the nitrate ion has a concentration exceeding a certain level (at least about 20 g/L) and is about 4 times the concentration of the phosphate ion.

(iii) Conversion on work surface: conversion from solution (ion)→sold (film) : Film components precipitating in the film formation are “metal” and “phosphate”.

The “metal” is reduced and precipitated from the condition under which the nitrate is dissolved. When the amount of the nitrate component (nitrate ion+metal ion) is small, the dissolved ion concentration is lower, so that current efficiency drops and precipitation efficiency drops, as well. Therefore, the treatment bath must have a predetermined concentration of the nitrate component. This is also represented in (ii) as described above.

Precipitation of the phosphate occurs as the phosphoric acid component (H₃PO₄ or H₂PO₄ ⁻) dissociates and changes to PO₄ ³⁻, thereby forming phosphate (Zn₃(PO₄)₂, etc) crystals as the film. It is therefore obvious that the precipitation process (level of necessary energy, etc) is different depending on whether the condition of phosphoric acid inside the treatment bath is H₃PO₄ or H₂PO₄ ⁻. In other words, it is easier to dissociate from H₂PO₄ ⁻ to PO₄ ³⁻ than from H₃PO₄ to PO₄ ³⁻. To improve the electrolytic reaction efficiency, it is therefore effective to bring the treatment bath into the condition under which phosphoric acid contains H₂PO₄ ⁻ as much as possible. In other words, the precipitation efficiency of the phosphate can be improved by using the treatment bath in which dissociation of H₃PO₄ →H₂PO₄ ⁻ is promoted by dissolving ZnO (zinc oxide), etc, in H₃PO₄ in the solution state to dissolve the zinc ion (Zn²⁺).

Other means for improving electrolytic reaction efficiency will be explained.

The existence of metal ions dissolved from the nitrate in an amount of at least 20 g/L is directed to improving the electrolytic reaction efficiency by increasing the concentration of the electrolytic component of the treatment bath.

The oxidation reaction potential (ORP: hydrogen standard electrode potential) of at least 770 mV in the phosphating treatment bath represents a control item associated with the electrochemical reaction of the iron expressed by: Fe²⁺

Fe³⁺ +e:0.77 V   (1)

The case where ORP of the treatment bath is at least 770 mV indicates that the condition of the iron ion inside the treatment bath is fully in the state of Fe³⁺ from the formula (1). This indicates also that the iron ions inside the treatment bath do not change. To improve reaction efficiency, it is necessary to control the condition of the chemical components of the treatment bath.

The current of at least 2 A/dm² at the electrolytic voltage of 6 V or below represents a feature of the present invention in comparison with the prior art (JP-A-2000-234200 and JP-A-2002-322593). The prior art technologies have no actual records of requiring a current of at least 2 A/dm² at 6 V or below.

Similarly, a current of at least 20 A/dm² at the electrolytic voltage of 15 V or below represents a feature of the present invention in comparison with the prior art (JP-A-2000-234200 and JP-A-2002-322593). The prior art technologies have no actual records of requiring a current of at least 20 A/dm² at 15 V or below.

A further object of the invention is to apply afresh the phosphating treatment to warm or hot forging lubrication treatment. Namely, the invention provides the following as means for achieving the object.

(1) An electrolytic phosphating treatment method for forming a film containing a metal precipitating from a nitrate and a phosphate by executing electrolysis of a metal, that is the same as a metal of a nitrate of a treatment bath, as an electrode and a work by using a D.C. power source, the treatment bath comprising phosphoric acid; zinc, iron or manganese as a metal capable of dissolving in a phosphoric acid solution and dissociating phosphoric acid; and a solution dissolving therein a nitrate of a metal to become a film component, wherein aninons other than nitrate ions and metal ions other than the metal ions to become the film component are present at not greater than 0.5 g/L, the metal ions dissolved from the nitrate are present at greater than 10 g/L and the phosphoric acid content and the phosphate ion content are not greater than ½ of the metal ion dissolved from the nitrate.

(2) An electrolytic phosphating treatment method for forming a film containing a metal precipitating from a nitrate and a phosphate by executing electrolysis between a metal, that is the same as a metal of a nitrate of a treatment bath as an electrode, and a work by using a D.C. power source, the treatment bath comprising a phosphate solution prepared by dissolving zinc in a phosphoric acid solution; phosphoric acid and phosphate ions; zinc ions as a metal capable of dissociating, and dissolving in, phosphoric acid; and a solution containing a nitrate of nickel, cobalt, manganese, copper or zinc; wherein anions other than nitrate ions and phosphate ions and metal ions other than the metal ions to become the film component are not greater than 0.5 g/L, respectively, the content of metal ions dissolved from the nitrate is greater than 10 g/L and the phosphoric acid and the phosphate ion contents are not greater than ½ of the metal.

(3) The electrolytic phosphating treatment method according to (1) or (2), wherein the metal ion dissolving from the nitrate is at least 20 g/L and phosphoric acid and the phosphate ion are ½ of the metal ion dissolving from the nitrate.

(4) The electrolytic phosphating treatment method according to (1) or (2), wherein an oxidation reduction potential (ORP: hydrogen standard electrode potential) of the phosphating treatment bath is at least 770 mV.

(5) The electrolytic phosphating treatment method according to (1) or (2), wherein an electrolytic voltage is 6 V or below and an electrolytic current is at least 2 A/dm².

(6) The electrolytic phosphating treatment method according to (1) or (2), wherein an electrolytic voltage is 15 V or below and an electrolytic current is at least 20 A/dm².

(7) A lubrication treatment method for warm or hot forging of a metal, characterized by using a work, the work having a film having a lubrication function, and being formed by the steps of:

forming a film formed of a phosphate plus a metal constituted by a metal having a melting point higher than the temperature applied to the work during warm or hot forging of a metal and a phosphate on a surface of the work; and

supporting a lubricant on the formation film.

(8) The lubrication treatment method for warm or hot forging, wherein a phosphating treatment film to be formed on a surface of a work and constituted by a phosphate plus a metal is a phosphating treatment film according to item (1) or (2).

(9) The lubrication treatment method for warm or hot forging according to (7) or (8), wherein the lubricant is an organic compound containing an organic fatty acid salt or an inorganic high molecular weight compound having a multi-layered structure.

(10) The lubrication treatment method for warm or hot forging according to (9), wherein the lubricant is a stearate, graphite, molybdenum sulfide or mica.

(11) A warm or hot forging method comprising the steps of:

forming a phosphate+metal film constituted by a metal having a melting point not lower than a temperature applied to a work during warm or hot forging of a metal and a phosphate;

supporting a lubricant on the film to form the work having the film having a lubrication function in warm or hot forging; and

conducting warm or hot forging.

(12) The warm or hot forging method according to (11), wherein the phosphate+metal film contains a phosphate that does not contain water of crystallization by differential thermal analysis.

The effect of the present invention is, in the first place, the provision of an efficient method when the metal+phosphate film is formed by the electrolytic treatment method. In other words, the method of the invention can cause a greater quantity of current to flow than the treatment methods of the prior art and can therefore shorten the treatment time.

The second effect of the present invention is that when the “metal+phosphate” formation film is formed by the electrolytic treatment method, the method of the invention can form the film at a lower impressed voltage than in the prior art methods. The phosphating treatment film according to the present invention can be formed at an impressed voltage of 1.5 to 6 V for which no actual records have been found. Lowering of the impressed voltage leads to suppression of the decomposition of the treatment bath. Consequently, stability of the treatment bath can be drastically improved; hence, the formation of sludge can be efficiently suppressed. Lowering of the impressed voltage can reduce the diameter of the crystal grains of the film to be formed. A smaller crystal grain will contribute to the improvement of the corrosion resistance when used for coating foundation.

The third effect is to expand the application to a new field by making the most of the features of the metal+phosphate treatment film. The phosphating treatment film formed by the present invention has heat resistance. Therefore, the phosphating treatment film can be applied to the field of the lubrication treatment for warm or hot forging to which films, obtained from the non-electrolytic treatment of the prior art, have not been applied in the past.

This new lubrication treatment uses the phosphating treatment film which chemically reacts with the surface of the work in the same way as in the lubrication treatment for cold forging, and covers the surface with a lubricant to form the film. Consequently, a material such as an organic fatty acid salt (e.g. sodium stearate) that has not been applicable in the past can be used as the lubricant for warm forging.

After the work is heated to about 250° C., coating can be done without heating for the lubricant, such as graphite, that has been physically applied to the work. Adhesion to the work can be improved because the lubricant, such as graphite, adheres to the phosphating treatment film but not to the surface of heated iron. This is a desirable lubrication property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the flows of a current and ions in an electrolytic treatment.

FIG. 2 is an SEM photograph of a film formed in Example 1 (1000 times).

FIG. 3 is an SEM photograph of a film formed in Example 2 (1000 times)

FIG. 4 is an SEM photograph of a film formed in Example 3 (1000 times).

FIG. 5 is an SEM photograph of a film formed in Example 4 (1000 times).

FIG. 6 is an SEM photograph of a film formed in Example 5 (1000 times).

FIG. 7 is an SEM photograph of a film formed in Comparative Example 1 (1000 times).

FIG. 8 shows an appearance after the passage of 2,000 hours after a brine spray test conducted after a formation treatment and electro-deposition coating (film thickness of 15 μ).

FIG. 9 is a schematic view of a work for forging (lower body).

FIG. 10 shows the conditions before and after hot forging of the work (lower body).

FIG. 11 is a differential thermal analysis diagram of phosphating treatment films used in Examples 6 to 8 of the present invention.

FIG. 12 is a differential thermal analysis diagram of the phosphating treatment film of Comparative Example 4.

FIG. 13 is SEM photographs of phosphating treatment films of Examples 6 to 7.

FIG. 14 is an SEM photograph of a phosphating treatment film of Comparative Example 4.

FIG. 15 shows the appearance before warm forging (NB cylinder) in Example 9 and Comparative Example 5.

FIG. 16 shows the appearance after warm forging (NB cylinder) in Example 5 and Comparative Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The film to be formed by the electrolytic treatment according to the present invention is a metal+phosphate film.

The metal is dissolved and supplied in the form of a nitrate in a treatment bath. The metal is reduced by electrolysis and precipitates. In other words, it precipitates in the following formula: M ²⁺+2e→M°  (2)

The phosphate precipitates as a metal salt as phosphoric acid dissociates. The metal salt precipitating thereby is limited to the kind of metals that can dissociate phosphoric acid and can be dissolved. The kind of metals is limited to zinc, iron or manganese. In the present invention, however, the metal that can dissociate phosphoric acid and can be dissolved is suitably zinc from the aspect of safety of the treatment bath.

First, the composition of the phosphate treatment bath will be described.

The components that constitute the phosphating treatment bath include phosphoric acid, a portion in which zinc is dissolved while dissociating phosphoric acid and is dissolved while associating with phosphate ion and a portion in which nitrates of nickel, cobalt, manganese, copper and zinc are dissolved. When these components are classified by the kind of anions, they can be classified into a portion of the phosphate ion system and a portion of nitrate ion system. The other kinds of ions are miscellaneous ions and their amount is limited to 0.5 g/L or below.

When the components constituting the treatment bath are expressed by the proportion of the kind of the anions described above in the phosphating treatment bath according to the present invention, the relation becomes nitrate ion system>phosphate ion system, the metal nitrate is at least 10 g/L and the sum of the phosphoric acid and the phosphate ion is not greater than ½ of the metal nitrate.

In the phosphating treatment bath according to the invention, the metal nitrate is more preferably at least 20 g/L and the sum of phosphoric acid and the phosphate ion is not greater ½ of the metal nitrate.

Incidentally, in the electrolytic treatment of aluminum materials, a necessary amount of F (fluorine) ions such as 1 g/L or below is permissible for preventing the formation of an oxide film on the surface of aluminum.

Next, the electrode materials will be explained. The electrode material uses a metal that is to be precipitated. The metal that is to be reduced and precipitated is the same as the metal that is supplied as the nitrate to the treatment bath. Therefore, the material of the metal electrode is nickel, cobalt, manganese, copper and zinc or their alloys.

Next, the electrolytic treatment method will be described. The electrolytic treatment is carried out by constituting an electrolytic treatment system shown in FIG. 1 by using the treatment bath and electrode materials described above and a D.C. power source. The electrolytic treatment generally includes anodic electrolytic treatment by using the work as a anode and an iron electrode as a cathode and then cathodic electrolytic treatment by using a metal of the nitrate of the treatment bath as the anode and the work as the cathode. The anodic treatment may be omitted. Generally, the electrode material is different between the anodic treatment and the cathodic treatment and a plurality of materials can be used. The electrolytic phosphating treatment bath generally includes an electrolytic treatment bath and a tank in which the treatment is not carried out so that the solution can be circulated between them. In this instance, the treatment bath must have a construction capable of removing molecular nitrogen oxides (NOx) that are formed by the reduction of the nitrate ions generated in the treatment bath.

Next, other contrivances will be explained. It is preferred to measure the ORP (oxidation-reduction potential) of the treatment bath and to keep it at 770 mV or more. This is necessary for preventing the iron ions dissolving from the electrode and the work and into the treatment bath. A bath having ORP of 770 mV or more does not contain, in principle, Fe²⁺ from the formula (1). In other words, when the treatment bath according to the invention mainly containing the nitrate ion contains Fe²+ (that is, when ORP is lower than 770 mV), oxidation to Fe 3+ occurs inside the treatment bath and solubility of the Fe ions drops in the treatment bath, so that sludge is formed.

Therefore, the ORP of the treatment bath at 770 mV or more is important for controlling Fe2+ inside the treatment bath, that is, the quantity of the iron ions dissolving from the electrode and the work as represented by the formula (3): Fe→Fe²⁺+2e  (3)

Consequently, ORP control of the treatment bath is preferably carried out.

The electrolytic treatment is substantially carried out at a voltage of 15 V or below and more preferably, 6 V or below.

Next, the application of the electrolytic phosphating treatment according to the invention includes the application to warm (or hot) forging/lubrication treatment. A best mode will be explained.

According to the lubrication treatment for warm forging in the present invention, there is formed a work in which a phosphate+metal film, including a metal having a melting point higher than the temperature applied to the work during warm forging of the metal and the phosphate, is formed on the surface of the work and the lubricant is supported on the coat, and the film of which has the lubrication function in warm forging. The formation of the phosphating treatment film consisting of the “phosphate+metal” and formed on the surface of the work is carried out by the electrolytic system.

The lubrication function in the forging of the metal has the following mechanism. When the mold and the work (metal) come into mutual contact and the work undergoes plastic deformation, the lubrication film (foundation film+lubrication film) covering the surface of the work is molten and fluidized in a temperature range of forging and so changes as to follow up the plastic deformation of the work, thereby preventing the direct contact of the work and the mold. The foundation film constituting the lubrication film is generally an inorganic compound containing a phosphate, and the lubricant is preferably an organic compound generally softened between 200 to 1,000° C. or an inorganic compound having a laminar structure. Suitable examples include organic fatty acid salts such as sodium stearate, fluorocarbon resins, molybdenum disulfide and graphite.

The reason why the phosphate compound is selected as the foundation film for the lubrication treatment for cold forging is as follows. When the mold and the work (metal) come into contact and the work undergoes plastic deformation within the temperature range of cold forging, the lubrication film (foundation film+lubrication film) covering the surface of the work is molten and fluidized in the temperature range of cold forging and can change in such a fashion as to follow the plastic deformation of the work. Therefore, the function required for the phosphating treatment film in cold forging is to secure suitable adhesion with the work (metal) and to uniformly distribute, and to maintain the distribution of, the lubricant such as sodium stearate.

When the mold and the work (metal) come into mutual contact and the work undergoes plastic deformation in the temperature range of forging, the lubricant does not react with the mold as the counter-part but exists stably. Because the lubricant has fluidity, it can follow the plastic deformation (elongation) of the work, can prevent the direct contact between the mold and the work and can also prevent deterioration of the mold.

Next, the foundation treatment film of the forging/lubrication treatment will be further explained. The requirements for the foundation film are retention of adhesion with blank metal and uniform retention of lubricant. The foundation treatment film is not necessary if the lubricant can retain adhesion with the blank metal through a chemical reaction. As such a lubricant does not exist, however, the foundation treatment is necessary.

Adhesion with the blank metal required for the foundation treatment is an adhesion such that when the mold and the work (metal) come into mutual contact and the work undergoes plastic deformation in the temperature range of forging, the lubrication film (foundation film+lubrication film) covering the surface of the work is softened and fluidized in the temperature range of forging, follows the plastic deformation of the work and changes.

Therefore, excessive adhesion of the foundation treatment film with the blank metal is not suitable and suitable adhesion is required.

The foundation treatment film is also required to uniformly retain the lubricant. Lubricants in general are organic fatty acid salts and inorganic high molecular weight compounds having multi-layered structures (graphite, for example) and do not have chemical affinity with the metal surface. (Therefore, the lubricant cannot be formed directly on the metal). In contrast, as the phosphate has chemical affinity with the lubricant described above, it can retain the lubricant.

As described above, the lubrication foundation treatment film exists between the blank metal and the lubricant having mutually different properties and plays the role of combining them together. This is an important function.

It is the temperature range that is to be taken into consideration in the lubrication treatment of forging. The forging temperatures are different among cold forging, warm forging and hot forging. The forging temperature is also different in warm forging depending on the kind of metals. Therefore, the classification of lubrication property and fluidity in the temperature range of forging is substantially as follows: Forging:

(i) cold forging: forging temperature 100 to 250° C.

(ii) warm forging:

(ii-1) steel: forging temperature 300 to 1,000° C.

(ii-2) non-ferrous metal: forging temperature 200 to 600° C.

Therefore, the temperature for the lubrication treatment (foundation film+lubrication film) is decided in consideration of the temperatures listed above.

The reason why the phosphate compound is selected as the foundation film of cold forging/lubrication treatment of the steel is as follows. When the mold and the work (metal) come into mutual contact in the temperature range of cold forging and the work undergoes plastic deformation, the lubrication film (foundation film+lubrication film) covering the surface of the work is softened and fluidized in the temperature range of cold forging and can exhibit the function of changing while following the plastic deformation of the work. Therefore, the functions required for the phosphating treatment film of the lubrication treatment for cold forging are suitable adhesion with the work (metal), uniform distribution of the lubricant and the retention of this distribution.

The forging temperature must be taken into consideration when the lubrication foundation film capable of being applied to warm forging is considered. In other words, it is desired that the foundation film does not fall off from the blank even when heated to a temperature above 200° C. but follows the plastic deformation of the blank. Chemical affinity of the phosphating treatment film with the lubricant has been confirmed in the past. However, the film obtained by the conventional non-electrolytic treatment has not been applied to the foundation treatment for warm forging because, according to a conventional method, the phosphating treatment film is decomposed and dissociates from the work when the work is heated to a temperature of 200° C. or above.

The phosphating treatment film obtained by the non-electrolytic treatment of the prior art has the form of crystal grains containing water of crystallization such as Zn₃(PO₄)₂-4H₂O and having a size of about 50 μm. It is presumed that water of crystallization dissociates with the temperature rise and the chemical structure of the film of the large crystal grains is destroyed. Therefore, the phosphating treatment film formed by the non-electrolytic treatment does not have heat resistance.

The phosphating treatment film applied to lubrication treatment for warm forging desirably has heat resistance. The phosphate+metal treatment film obtained by the electrolytic treatment of the invention has the heat resistance that can be applied to warm forging. This film contains large amounts of metals that are reduced and precipitated, and also contains the phosphate.

The film formed by the electrolytic treatment of the invention has affinity with the lubricant because the film is the phosphate+metal treatment film and contains the phosphate. Therefore, the film according to the invention has the heat resistance and affinity with the lubricant.

The formation of such a film can be conducted on the basis of the use of the treatment bath not containing metal ions other than the film components that is disclosed in JP-A-2000-234200.

In other words, the lubrication treatment for warm forging according to the invention for forming the phosphating treatment film consisting of the phosphate+metal on the surface of the work is carried out by the method that electrolyzes on the surface of the work inside the treatment bath constituted by phosphoric acid and phosphate ion; zinc ion as a metal capable of dissociating and dissolving in phosphoric acid; and a solution containing a nitrate of nickel, cobalt, manganese, copper or zinc.

Suitably, the formation of the phosphating treatment film, consisting of phosphate+metal and formed on the surface of the work, is carried out in the treatment bath in which the metal ion dissolving from the nitrate is at least 10 g/L and phosphoric acid and phosphate ion are not greater than ½ of the metal ion. Further suitably, the formation of the phosphating treatment film consisting of the phosphate+metal and formed on the surface of the work is carried out in the treatment bath in which the metal ion dissolved from the nitrate is at least 20 g/L and phosphoric acid and phosphate ion are not greater than ½ of the metal ion dissolved from the nitrate.

Next, the application of the film described above to warm forging will be explained. In the invention, the explanation will be given mainly on the example of the steel as described above but the invention can be applied to all the metal materials used for executing warm forging.

The term “warm forging” means those kinds of forging which execute forging after a metal material is heated to a temperature higher than room temperature. The heating temperature varies depending on the kind of the metals. Table 2 tabulates general warm and hot forging temperatures of various metals subjected to warm forging. TABLE 2 warm & hot melting point forging of metal: ° C. temperatures: ° C. remarks iron and 1535  300-1100 steel aluminum 660 200-450 and its alloy magnesium 648 200-450 and its alloy copper and 1083 200-600 its alloy

Next, the metal characteristics of the phosphate+metal film formed on the work and the condition of the treatment bath will be clarified. Table 3 tabulates those metals which can be contained in the phosphating treatment film. TABLE 3 precipitation- divalent-trivalent melting point dissolution reaction equilibrium of metal: ° potential: V potential: V C. M

M²⁺+ 2e M²⁺

M³⁺ + e Ni 1453 −0.257 — Mn 1244 −1.18 1.51 Co 1495 −0.277 1.92 Cu 1083 0.34 — Zn 419 −0.77 —

The first necessary condition corresponding to the phosphate+metal is the melting point of the metal. The metal contained in the film must have a melting point higher than the forging temperature of the work (refer to Table 2).

The second necessary condition is the behavior in the treatment bath for forming the film. In order for the metal to be taken into the film, the metal must be stably dissolved and exist as the divalent metal ion in the phosphating treatment bath. For this purpose, it is necessary that the charge of the metal does not easily change within the range of the oxidation reduction potential at which water, as the solvent, is not decomposed. In other words, the equilibrium of M²⁺⇄M³⁺+e does not exist.

(Solubility drops when the metal ions change to M³⁺ in the relation M²⁺→M³⁺+e. Consequently, the sludge is formed in the treatment bath. The sludge impedes stability of the treatment bath as the solution and is not permissible).

The third condition is that the metal is not affected by hydrolysis of water as the solvent. The decomposition of water as the electrochemical reaction occurs when the potential of the treatment bath exceeds the oxidation reduction potential represented by the following formulas (4) and (5):

Anodic reaction: H₂+2OH⁻2H₂O+2e: −0.83 V   (4) Cathodic reaction: O₂+4H⁺+4 e2H₂O: 1.23 V   (5)

Therefore, as long as the equilibrium potential of the metal component inside the treatment bath, that is, M²⁺

M³⁺+e, is within the range of the potential represented by the formulas (4) and (5), the metal component ion has the possibility of changing from the condition M²⁺ to the condition M³⁺ inside the treatment bath. The occurrence of such a change is not preferred.

The metals tabulated in Table 3 do not have the equilibrium potential M²⁺

M³⁺+e within the range of −0.83 V to 1.23 V.

The fourth essential condition is that cathodic precipitation can be conducted without being affected by the electrolysis of water as the solvent. The relation M²⁺

M³⁺+e tabulated in Table 3 must be taken into consideration. In other words, when the cathodic precipitation of the metal ion, i.e. M²⁺+2e→M, is 0.83 V or below, the reaction of the cathodic decomposition reaction formula (4) of water as the solvent occurs preferentially and the cathodic precipitation of the metal ion is not possible in principle. Namely, when the precipitation-dissolution reaction potential of the metal shown in Table 3 is by far lower than −0.83 V, electrolytic precipitation from the aqueous solution is not possible. The precipitation-dissolution reaction potentials of the metals tabulated in Table 3 (Ni, Mn, Co, Cu, Zn) other than Mn are higher than −0.83 V and precipitation is possible. The potential of Mn is only slightly lower than −0.83 V and precipitation is possible.

Therefore, as the metals tabulated in Table 3 satisfy the three conditions described above, the phosphate+metal treatment film can be formed by the electrolytic treatment. However, it is necessary to suitably use the precipitation metal in accordance with the kind of materials to be forged.

Next, the function of the lubricant and its best mode will be described. The lubricant that is formed on the work and has been used in the past for warm forging, such as graphite, can be used in the invention. An organic fatty acid salt can be used as a novel lubricant for warm forging. This is because the phosphating treatment film having the heat resistance is used for the foundation treatment.

The function of the lubricant is to prevent the direct contact between the work and the mold during warm forging. In the case of the iron and steel, graphite has been used as the lubricant to be directly applied to the work after heating to about 250° C. However, graphite only adheres physically to the work and does not have reliable adhesion. Therefore, the work is immediately heated to about 800° C. and subjected to warm forging.

The formation of the lubricant film on the work becomes easy when the phosphating treatment film having the heat resistance is formed as the foundation film. This is because the lubricant has chemical affinity (analogous properties) to the phosphating treatment film. Therefore, the lubricant can be dispersed, attached and allowed to-adhere to the surface of the treatment film more uniformly and more reliably than the surface of iron and steel materials.

In the warm forging method according to the invention, the phosphating treatment film having the heat resistance is formed and the lubricant is applied onto the film. Therefore, the organic fatty acid salt can be used as the novel lubricant. In other words, the fatty acid salts such as sodium stearate that have been used in the past for cold forging can be used for warm forging.

In other words, in the warm forging lubrication treatment according to the invention, the work having the lubrication function in warm forging is formed in which the phosphate+metal film constituted by the metal having a melting point equal to or higher than the temperature applied to the work during warm forging of the metal and the phosphate is formed, the lubricant as the organic fatty acid salt and the inorganic high molecular weight compound having the multi-layered structure is supported on the coat, and warm forging is carried out by heating this work. Warm forging itself is basically carried out in the same way as the existing methods. A spray of the lubricant onto the warm or hot forging mold has also the function of cooling the mold and is necessary.

Examples 1 to 5:

I. Improvement of Efficiency of Electrolytic Phosphating Treatment

Table 4 shows the treatment bath conditions in Examples 1 to 5 and Comparative Example 1. TABLE 4 bath of bath of Examples 1 Comparative to 5 Example 1 bath phosphate ion: g/L 12 12 composition zinc ion: g/L 10 10 nitrate ion: g/L 150 60 nickel ion: g/L 54 22 total acidity: pt. 200 45 electro- pH 0.8-1.0 1.6-1.8 chemical index ORP: shown by 670 mV 676 mV of treatment silver/silver bath chloride electrode

In Comparative Example, the concentrations of phosphoric acid and phosphate ion are higher than ½ of the metal ion (Ni). In this point, the treatment bath is out of the range of the bath of the present invention.

The electrolytic phosphating treatment is carried out in these treatment baths. Table 5 shows an outline. TABLE 5 trial product/test condition test No. Comparative Examples 1-5 Example 1 1 2 3 4 5 1 test material cold rolled steel sheet: SPCC material clutch (50 × 50 × 1 mm) component: stator: spcc material treatment step degreasing → washing with water → surface Table 6 conditioning → electrolytic phosphating treatment → washing with water → drying electrolytic phosphating bath of Example of Table 1 bath of treatment bath Comparative Example 1 of Table 1 electrolytic anodic immersed for 5 secs 3 V × 0.01 A/dm² × 12 sec condition treatment cathodic 1.8 V × 3 V × 4 V × 5 V × 6 V × 8 V × 1.5 A/dm² × (9 sec↑, treatment 2.5 A × 5 A × 3.4 A × 7 A × 7 A × 77 sec→) (current: (5 sec↑, (5 sec↑, (5 sec↑, (5 sec↑, (5 sec↑, dm² 40 sec→) 40 sec→) 40 sec→) 40 sec→) 20 sec→) calculation value) total 50 sec 30 sec 98 sec treatment time resulting film 1 5 3 7 5 2 film thickness: μm appear- gray gray black ance SEM × FIGS. 1-5 1,000 times

Incidentally, the film thickness is measured by using an electromagnetic film thickness meter (LE-300J, K.K. Ketto Kagaku Kenkyujo).

FIGS. 2 to 7 show the SEM photographs (1,000 times) of the films formed in Examples 1 to 5 and Comparative Example 1, respectively. Because the voltage is small in Example 1, a current is small, too, and film formation is 10 not sufficient. Films are formed in Examples 2 to 5.

Comparative Example 1 represents the result in mass production equipment. Table 6 shows the process steps of Comparative Examples. TABLE 6 step: time (sec) transfer (sec) time total: sec. step content remarks 1 degreasing: 100 50 150 55° C.: alkali degreasing 2 degreasing: 100 50 150 55° C.: alkali degreasing 3 washing with 50 150 water: 100 4 washing with 50 150 water: 100 5 phosphating: 100 50 150 electrolytic (1.5 A/dm²) treatment: 8 V × 3 A/ piece 6 washing with 50 150 water: 100 7 pure water spray: 50 150 spray for 45 sec 45 and leave-standing for balance 8 electro-deposition 50 150 lead-free paint: voltage 200 V coating: 100 film thickness of 15 μ or more 9 washing with pure 50 150 water: 100 10 washing with pure 50 150 water: 100 11 washing with pure 50 150 water: 100 12 pure water spray: 50 150 spray for 45 sec 100 and leave-standing for balance time: sub-total 1800 13 temperature elevation: 1200 = 20 min. 1200 inclusive of transfer and replace 14 baking: 1500 = 25 min. 1500 200° C. 15 cooling: 1500 = 25 min 1500 inclusive of transfer and replace total: time = lead time 6000 = 100 min —

In Comparative Example 1, the work is a clutch component stator and FIG. 8 shows the appearance after the phosphating treatment→electro-deposition film (film thickness: 15 μ) and salt spray test for 2,000 hours. Peeling of the film from a film cross-cut portion does not occur and the corrosion resistance is fair.

Incidentally, the paint is electro-deposition paint “Power-Nix” 110 black, lead-free cation electro-deposition paint of Nippon Paint K. K.

Next, electro-deposition films of Examples 1 to 5 will be described.

Coating condition: Power-Nix 110 Black (lead-free cation electro-deposition)

Coating condition:

The following three kinds are used.

A: electro-deposition time: 45 sec (including 10 sec for rise voltage control)

B: electro-deposition time: 60 sec (including 11 sec for rise voltage control)

C: electro-deposition time: 90 sec (including 12 sec for rise voltage control)

Coating temperature: 30° C., baking-drying temperature: 160° C.×10 min

Coating voltage: 150 V

The coat thickness of each Example after coating→baking is shown in Table 7 (unit: μm). TABLE 7 formation treatment condition coating condition Example 1 2 3 4 5 A  8 μm 6 7 7 9 B 10 8 10 9 12 C 16 12 16 17 17

The thickness of the coat film greatly depends on the electro-deposition coating time rather than on the formation condition of the phosphating film.

Table 8 shows the result of the salt spray test of the coating products described above. The numeral shown in FIG. 8 represents the peel width by mm from the line formed by cutting the coat film. The smaller the value, the better the result.

The result shown in Table 8 represents that the corrosion resistance of the film depends more greatly on the formation treatment condition than on the coating film thickness. In Examples of the electrolytic treatment products, the corrosion resistance of the film remains at the existing level even when the film thickness is small with the exception of a voltage of 1.8 V. TABLE 8 coating brine spray test condition: time 408H 1008H 1248H 1608H 2016H 45 sec Example 1 2 10 11 15 15 Example 2 0 0 0 0 0 Example 3 0 0 0 0 0 Example 4 0 0 0 0 0 Example 5 0 3 10 10 15 60 sec Example 1 0 5 5 15 15 Example 2 0 0 0 0 0 Example 3 0 0 0 0 0 Example 4 0 0 0 0 0 Example 5 0 0 0 0 0 90 sec Example 1 0 3 3 15 15 Example 2 0 0 0 0 0 Example 3 0 0 0 0 0 Example 4 0 0 0 0 0 Example 5 0 0 0 0 0

It can be understood that Examples according to the invention can execute the treatment (formation treatment, electro-deposition coating, baking) within ½ of the time of Comparative Example. This can be achieved by the combination of the coating condition A described above with Examples 1 to 5. According to these combinations, the thickness of the film becomes ½ of the thickness of Comparative Example but the corrosion resistance can maintain the level of Comparative Example 1.

The electrolytic voltage is 3 to 6 V and the treatment at a lower voltage than 8 V of Comparative Example 1 becomes possible. Therefore, from the aspect of the electrolytic voltage, decomposition of the treatment bath components is suppressed. In other words, the formation of the sludge can be much more suppressed.

Examples 6 to 8

II. Application to Warm Forging

A car engine component (lower body: material SCM415) is used. FIG. 9 shows the condition before warm forging and FIG. 10 shows the condition before and after warm forging.

Table 9 shows the process steps of warm forging in Examples 6 to 8 and Comparative Example 2. However, washing with water and washing with hot water are omitted. In warm forging press, a solid lubricant (graphite) is sprayed to a press mold under the same condition in Examples 6 to 8 and Comparative Example 2. TABLE 9 Comparative step Example 6 Example 7 Example 8 Example 2 Pre-step Coil material having phosphating treatment film + lubricant (stearate) formed as lubrication treatment is cold forged. 1 shot blast ◯ ◯ ◯ - (nil) 2 degreasing ◯ ◯ ◯ - (nil) 3 electrolytic phosphating ◯ ◯ ◯ - (nil) formation treatment: metal + phosphate 4 lubrication treatment ◯: ◯: ◯: - (nil) graphite “Moricoat” synthetic mica molybdenum disulfide 5 heating: 850° C. ◯: induction heating 6 warm forging press ◯: Nippon Atison K. K., “Aquaduck”, 10% aqueous solution is applied by spraying.

The difference of Examples 6 to 8 is only the difference of the lubricant. The difference of Examples 6 to 8 from Comparative Example 2 is that Examples execute the “metal+phosphate” foundation treatment and the lubrication treatment inclusive of shot blast (executed by removing the pre-step phosphating formation treatment film), whereas the Comparative Examples do not include such treatments.

The detail of the electrolytic phosphating treatment is as follows. The composition of the treatment bath contains phosphoric acid and phosphate ion: 15 g/L, zinc ion: 10 g/L, Ni ion: 51 g/L and nitrate ion: 157 g/L. The work (lower body) shown in FIG. 9 is placed as the negative electrode into the treatment bath and a Ni plate, as a positive plate. After the work is immersed for 10 seconds without the application of the voltage, a voltage is raised to 13 V in the course of 5 seconds and a current is caused to flow at 28 to 32 A for 25 seconds through one work (surface area of 1.2 dm²). The temperature at that time is 30 to 34° C. A film of phosphate+Ni having a black gray color is formed in this way on the surface of the work.

The lubrication treatment is carried out by immersing the work into an aqueous solution to form a film. The outline is shown in Table 10. TABLE 10 Example 6 Example 7 Example 8 composition graphite: molybdenum synthetic Nippon Atison K. K., disulfide: mica: “Delta-forge”, Nihon Corp Chemical F818 30% Parkerizing K.K., Co. K.K., “Palub”, “Somashiff”, LUB4642 S1ME 30% temperature 60-80° C. 60-80° C. 60-80° C. treatment immersion for immersion for immersion for time 30 sec 30 sec 30 sec

Table 11 shows the difference of the machining load in warm forging press. TABLE 11 Comparative Example 6 Example 7 Example 8 Example 2 machining 40 40 40 70 load: 10 KN

The machining load is remarkably different between Examples and Comparative Example. In examples, the 15 machining load is low and excellent. This represents that lubrication performance is greatly different between the case where the lubrication film is formed on the work (Examples) and the case where the lubrication film is not formed (Comparative Example). It is obvious that the present invention is effective.

III. Comparison of Composition of Phosphating Treatment Film

The difference of Examples 6 to 8 of the present invention from the electrolytic phosphating treatment film of the prior art will be demonstrated. Examples 1 and 4 described in JP-A-2000-234200 are cited as Comparative Example 3 to demonstrate the film obtained by the electrolytic treatment of the prior art. TABLE 12 Comparative Example 3 Example 1 of Example 4 of Exam- JP-A-2000- JP-A-2000- ples 232400 232400 6-8 treatment phosphate ion 7.6 2.8 12.3 bath nitrate ion 12 10.1 150 composition Ni ion 5.5 3.8 51 g/L Zn ion 0.4 0.4 9.1 (Ni + Zn)/ 0.78 1.5 4.9 phosphate ion film Ni 6.1 9.6 22.2 composition Zn 1.9 8.6 27.6 Wt % P 2.9 19 5.9 Ni/P 2.1 0.5 3.8 (Ni + Zn)/P 2.8 0.96 8.4

The difference between Examples 6 to 8 and Comparative Example 3 is the proportion of the metal component to phosphoric acid or phosphorus (P) in both treatment bath composition and film composition.

Examples of the present invention have greater proportion of the metal component in the treatment bath composition and the film composition than in Comparative Example 3. In other words, the film of the present invention is a film having a large metal component. In any case, the difference from the prior art example is distinctive.

IV. Comparison of Heat Resistance of Phosphate Formation Coat

Next, the heat resistance of the film is represented by the result of DSC: differential thermal analysis.

FIG. 11: diagram of differential thermal analysis of Examples 6 to 8 (phosphating treatment film for warm forging from electrolytic treatment)

FIG. 12: diagram of differential thermal analysis of Comparative Example 4 (phosphating treatment film from non-electrolytic treatment)

Comparative Example 4 represents the film produced by the conventional non-electrolytic system. The phosphating formation treatment bath is prepared by adjusting “Pal-bond” 3684X, a formation treatment chemical from Nihon Pakerizing K. K., under predetermined conditions. A cold rolled steel sheet is immersed in the treatment bath (80° C.) for 10 minutes to form a film. FIG. 12 is a differential thermal analysis diagram of the film and FIG. 14 is an SEM photograph of the film.

FIG. 11 is a differential thermal analysis diagram of a phosphating film structure used in Examples 6 to 8 of the present invention. In other words, it is a phosphating film produced by the electrolytic treatment for warm forging of the steel materials.

FIG. 12 is a differential thermal analysis diagram of a phosphating treatment film structure of the prior art used for cold forging of iron and steel materials. In other words, it is a differential thermal analysis diagram of a phosphate film produced by the non-electrolytic treatment system.

The great difference between FIG. 11 and FIG. 12 is that whereas a change of a differential scanning calorie curve exists in a temperature range of 200° C. or below in FIG. 12, such a phenomenon cannot be observed in FIG. 11.

A large weight change (decrease) takes place during the temperature rise of up to 200° C. in the film of FIG. 12 produced by the non-electrolytic treatment. This large change of the differential scanning calorie curve represents a large change of the film structure. It is well known that the phosphating film obtained by the non-electrolytic treatment of the prior art exists in the form of the crystal containing the crystal of water (moisture salt): Zn₃(PO₄)₂·4H₂O. Therefore, the large change of the film structure results from fall-off of the crystal of water from the phosphate crystal owing to heat of up to 200° C. It is clear, when FIGS. 13 and 14 are examined, that the appearance of the film is different between the electrolytic treatment and the non-electrolytic treatment. Presumably, this difference of appearance is related to the film structure.

It is impossible from the observation described above to apply the phosphating treatment film formed by the non-electrolytic treatment of the prior art to the foundation film for warm forging in which the film is heated to a temperature of 500° C. or above. Consequently, the phosphating treatment film of the prior art has not been used for warm forging.

The result of the differential thermal analysis represents the weight change of the coat due to heating. The film formed by the non-electrolytic treatment (FIG. 12) exhibits a weight decrease of 9.78/11.062=0.884 till the absorption of the differential scanning calorie curve due to heating but the electrolytic treatment film of the present invention (FIG. 11) exhibits a slight change of 187° C. and its weight change remains at 13.57/13.804=0.983. This represents that the phosphating treatment film of the present invention is more effective in the heat resistance than the coat of the prior art.

EXAMPLE 9 Example Using Organic Fatty Acid Salt for Lubricant

A car engine component (NB cylinder: material SUJ2: Cr-containing alloy steel) is used. FIGS. 15 and 16 show the forms of the NB cylinder before and after warm forging, respectively.

Table 13 shows the warm forging steps of Example 9 and Comparative Example 5.

Incidentally, the lubricant is spray coated to the press mold under the same conditions as in warm forging for Example 9 and Comparative Example 5. TABLE 13 Comparative step Example 9 Example 5 1 shot blast ∘ — (nil) 2 degreasing ∘ — (nil) 3 surface ∘ — (nil) adjustment 4 electrolytic ∘ — (nil) phosphating treatment: metal + phosphate 5 lubrication ∘: sodium stearate — (nil) treatment 3-6%: 85° C. solution, 3 min. 6 heating: 850° C. ∘ ∘ 7 warm forging ∘ ∘ press

The difference between Example 9 and Comparative Example 5 is as follows. In Example 9, the foundation treatment of metal+phosphate and immersion into the sodium stearate solution as the lubrication treatment are carried out for the work after the shot blast (executed by removing a pre-step phosphating film) is conducted. In contrast, these treatments are not carried out in Comparative Example 5.

The electrolytic phosphating treatment in Example 9 is the same as that of Examples 6 to 8.

Table 14 shows the machining load in warm press forging. TABLE 14 Comparative Example 9 Example 5 machining load: 10 KN 120-150 130-160

The machining load of Example 9 is equal to that of Comparative Example 5. Example 9 is an example that uses sodium stearate as the lubricant of the work. This compound has no actual performance record as the lubrication coat for work in the prior art. The present invention demonstrates that sodium stearate can be applied to the lubrication treatment.

The electrolytic phosphating treatment method according to the invention can apply a greater current at a lower voltage than in the electrolytic treatment of the prior art. In other words, the method of the invention is an electrolytic phosphating treatment technology that has higher efficiency than the prior art technologies.

The present invention is effective for the lubrication treatment for warm forging. It has not been possible to apply the phosphating treatment film to the foundation treatment of the warm forging lubricant but the invention has developed a novel warm forging lubrication treatment system by developing the film capable of being applied to warm forging by utilizing the method of the invention that precipitates greater amounts of metals. It has been confirmed that the lubrication treatment thus developed can drastically lower the machining load during warm forging. Therefore, the method of the invention is a technology that can improve warm forging. 

1. An electrolytic phosphating treatment method for forming a film, containing a metal precipitating from a nitrate and a phosphate by executing electrolysis of a metal that is the same as a metal of a nitrate of a treatment bath as an electrode and a work by using a D.C. power source, the treatment bath comprising phosphoric acid; zinc, iron or manganese as a metal capable of dissolving in a phosphoric acid solution and dissociating phosphoric acid; and a solution dissolving therein a nitrate of a metal to become a film component, wherein anions other than nitrate ions and metal ions other than the metal ions to become the film component are present at not greater than 0.5 g/L, the metal ion dissolving from the nitrate is present at greater than 10 g/L and phosphoric acid and phosphate ion are present at not greater than ½ of the metal ion dissolving from the nitrate.
 2. An electrolytic phosphating treatment method for forming a film containing a metal precipitating from a nitrate and a phosphate by executing electrolysis between a metal that is the same as a metal of a nitrate of a treatment bath as an electrode and a work by using a D.C. power source, the treatment bath comprising a phosphate solution prepared by dissolving zinc in a phosphoric acid solution; phosphoric acid and phosphate ions; zinc ions as a metal capable of dissociating, and dissolving in, phosphoric acid; and a solution dissolving a nitrate of nickel, cobalt, manganese, copper or zinc; wherein anions other than nitrate ions and phosphate ions and metal ions other than the metal ions to become the film component are not greater than 0.5 g/L, respectively, the metal ion dissolving from the nitrate is greater than 10 g/L and phosphoric acid and phosphate ion are not greater than ½ of the metal.
 3. The electrolytic phosphating treatment method according to claim 1, wherein the metal ions dissolved from the nitrate are present at at least 20 g/L and phosphoric acid and the phosphate ion are present at ½ of the amount of the metal ions dissolved from the nitrate.
 4. The electrolytic phosphating treatment method according to claim 1, wherein an oxidation reduction potential (ORP: hydrogen standard electrode potential) of the phosphating treatment bath is at least 770 mV.
 5. The electrolytic phosphating treatment method according to claim 1, wherein an electrolytic voltage is 6 V or below and an electrolytic current is at least 2 A/dm².
 6. The electrolytic phosphating treatment method according to claim 1, wherein an electrolytic voltage is 15 V or below and an electrolytic current is at least 20 A/dm².
 7. A lubrication treatment method for warm or hot forging of a metal, characterized by using a work, the work having a film having a lubrication function and being formed by the steps of: forming a formation film formed of a phosphate plus a metal constituted by a metal having a melting point higher than the temperature applied to the work during warm or hot forging of a metal and a phosphate on a surface of the work; and supporting a lubricant on the formation film.
 8. The lubrication treatment method for warm or hot forging, wherein a phosphating treatment film to be formed on a surface of a work and constituted by a phosphate plus a metal is a phosphating treatment film according to claim
 1. 9. The lubrication treatment method for warm or hot forging according to claim 7, wherein the lubricant is an organic compound containing an organic fatty acid salt or an inorganic high molecular weight compound having a multi-layered structure.
 10. The lubrication treatment method for warm or hot forging according to claim 9, wherein the lubricant is a stearate, a graphite, molybdenum sulfide or a mica.
 11. A warm or hot forging method comprising the steps of: forming a phosphate+metal film constituted by a metal having a melting point not lower than a temperature applied to a work during warm or hot forging of a metal and a phosphate; supporting a lubricant on the film to form the work having the film having a lubrication function in warm or hot forging; and conducting warm or hot forging.
 12. The warm or hot forging method according to claim 11, wherein the phosphate+metal film contains a phosphate that does not contain water of crystallization by differential thermal analysis. 